Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $213.43   10.714%   $236.2969   $236.30   $236.30   $236.30  
  Purchase #2 $73.31   9.588%   $80.339   $80.34   $80.35   $80.30  
  Purchase #3 $101.82   7.316%   $109.2692   $109.27   $109.25   $109.30  
  Purchase #4 $187.65   7.352%   $201.446   $201.45   $201.45   $201.40  
  Purchase #5 $63.28   11.515%   $70.5667   $70.57   $70.55   $70.60  
  Purchase #6 $103.99   8.545%   $112.8759   $112.88   $112.90   $112.90  
  Purchase #7 $184.79   11.632%   $206.2848   $206.28   $206.30   $206.30  
  7 purchase totals = $928.27       $1,017.0785   $1,017.09   $1,017.10   $1,017.10